One method of fighting fires or controlling hazardous material (hazmat) spills is the process of spraying foam over the fire or spill. When fighting fires, foam sprayed over a fire cuts off the fire's oxygen supply thereby extinguishing the fire. In hazmat spill operations, foam is used to prevent toxic materials from contacting the atmosphere. By covering the material with foam, toxic fumes emitted from the material are prevented from entering the atmosphere. Similarly, the atmosphere does not contact the material and the oxygen source for any potential fire is eliminated.
In either application, emergency personnel (fire fighters) use a hand-held foamaker to spray foam onto either the fire or the spilled material. Fire fighters begin the operation by spraying foam to the target area from the greatest possible distance so as to pretect themselves from intense heat or exposure to toxic materials.
In order to reach the target from distances of 35 to 50 feet, the fire fighter must use a foam having a low expansion ratio (for example, 5-20 to 1), since foam having a high expansion ratio cannot be propelled over such a distance.
There are inherent disadvantages in the use of low expansion ratio foams. One disadvantage is that these foams do not cover as great a target area as do higher expansion ratio foams. Accordingly, it is necessary to use more foam concentrate and the application becomes costlier than when high expansion foams are applied.
After the first application of low expansion foam and control of the fire or spill is obtained, the fire fighters can move in closer to the target area to within a distance of 12 to 15 feet of the target. At this distance, the fire fighter can then use a foam having a higher expansion ratio (for example, 250-1000 to 1) to blanket the area. A foam having a higher expansion ratio covers more of the target area than the low expansion foam and provides a thicker insulation layer between the fire or spill and the atmosphere. Further, foams having high expansion ratios require less water and concentrate to cover the same area as the low expansion foam. Accordingly, high expansion foams are less costly to apply.
In hazmat spill control operations, the fire fighter must match the expansion ratio to the type of chemical spill. For example, the hazmat specialist would not use low expansion foam on a water reactive liquid at any time. Since the nature of the spill is usually unknown, the variable expansion ratio appliance concept permits the control of any type of hazmat spill using the same piece of equipment.
Hazmat material spills upon which low expansion foam would typically be used are flammable, water immiscible liquids. Medium expansion foams typically are used on flammable, water immiscible (polar) liquids, and high expansion foams are typically used on water reactive liquids and liquified gases.
In order for the fire fighter to apply a low expansion foam and then a high expansion foam, the fighter must use two different foam generating devices. Accordingly, it would be desirable to have one foam generating device that could produce foams having variable expansion ratios ranging from low to high. It is the intent of this invention to provide such an apparatus, whereby the expansion ratio of the foam can be varied by adjusting a nozzle in the foam generating apparatus.
A variable flow rate foam device is described in Williams, U.S. Pat. No. 4,497,442. The Williams device is complicated in design and operation and is used solely to vary the flow rate of foam that is discharged from the nozzle rather than the expansion ratio of the foam. The present invention provides a means to vary the expansion ratio of the foam while the Williams device is capable of only producing a foam having one expansion ratio. Additional foamaking devices that are capable of producing foam having only one expansion rate are disclosed in Silverman, U.S. Pat. No. 3,306,008 and Barnes, U.S. Pat. No. 3,482,638.